<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<button id="btn">我是一个按钮</button>
<script>

    var elementById = document.getElementById("btn");
    elementById.innerHTML = "我被修改了";

</script>

</body>
</html>
